Arc carbon



. V Patented Aug. 1, 1933 rarest or ies sac CARBON Merrill 3. Dorcas, Cleveland, Ohio, assignor to National Carbon Company, 1110., a Corporation of New York No Drawing.

Application January 27, 1928 Serial No. 250,069

2 Claims. (Cl. 176-134) This invention relates to electrodes for are lamps. and especially to electrodes which are adapted for use with a high intensity are to produce a light having a. color value similar to that i of an incandescent lamp.

When a direct current arc, the positive electrode of which consists of a cored arc carbon, is operated above a certain critical current density two related effects are produced, a relatively deep crater is formed; and

incandescent gas ball of extremely high intrinsic 'brilliancy. This effect is termed the high intensity eiiect and the current densityrequired to produce it is a function of the diameter of the carbon'and the composition of' the core.

Hitherto it has been supposed that it was impossible to produce color changes in the high intensity are by varying the electrode composition. This belief was based in part on theoretical considerations and in ment. I have found, however, that this'belief is incorrect and that emitted from a high intensity arc, is capable of modification by the use of suitable addition agents Such addiin the core of the positive electrode.

tion agents are the compounds of calcium and strontium. While various salts of these elements may be used I have found the halides, particularly the fluorides, well adapted for this purpose.

3 These addition agents are especially suitable for this use as by properly proportioning the same it is possible to obtain light from a high intensity are which has a color value similar to that emitted from an incandescent tungsten light. It is desirable to obtain such color, values, not only for the purpose of producing a light suchas people are accustomed to, but also for use in the projection of colored moving pictures and the taking of pictures whether for still or motion picture work. In the colored motion picture process the color-effect is obtained by either the additive or subtractive method. In either case two or more colors, usually red and green, are

used and it is diilicult to obtain natural colors for other than the pure reds and greens or other colors used. Various compromises have to be effected and these naturally vary with variations in the color value of the light used in projection. 'Bec ause large numbers of projectors using incandescent tungsten lights or the incandescent crater of a carbon are as the light source are in use, the manufacturers have based their process upon this light and alight source having any other color value gives an incorrect'color renderthere is in this crater an chromatic film is'useli.

part upon actual experiwith an emulsion containing dyes which render 755 I the color value of the light now extant could not be used with the high intensity projectors and a new process would have to be Worked out the smaller theaters which use incandescent lamps in their projectors. By modifying the color value of the light from the high-intensity are so that it approximates that of the incan- 7 descent lamp I have avoided this difiiculty.

Similarly in the taking of pictures, not only still, but more especially motion pictures, a pan- This film is sensitized the emulsion sensitive to lights of varying colors in such a manner that the black and white image produced in the positive gives a rendering which approximates that given by the human eye. The present panchromatic films give fairly good results if the illumination is provided by an incandescent source such as a tungsten moandescent bulb or the incandescent crater of a suitablecarbonarc and in order to use the high intensity are for lighting objects to be photo- 1 graphed it was necessary either to modify the color value of the high intensity are or towork out a new emulsion for panchromatic films. By this invention I have succeeded in modifying the high intensity are light to give a color value similar to that of the incandescent tungsten light. While I have found the carbon electrodes produced in accordance with my invention to be of especial value in connection with high intensity arcs, they are also adapted for use with current densities below those which produce the high intensity efiect described above with both direct and alternating current.

In order to produce a modified high intensity are light I form the positive carbons with a core containingcalcium and strontium. While various cores may be used I have found the following composition satisfactory: calcium fluoride 40 parts, strontium fluoridelO parts, sodium or potassiumsilicate 5 parts, carbon flour 45 parts, tar sufiicient to bind. In a particular instance a positive 11 millimeters in diameter was provided with a core of this composition having a diameter of approximately 5.5 millimeters and operated with a negative approximately 9 to make special films for them. The special films would however be unsuitable for I claim:

mm. in diameter. At '75 to 200 amperes the intensity are in which approximately half the high intensity effect was obtained, and the color core is composed of fluoride salts of calcium and value was a sufficiently close approximation, to strontium in a ratio of substantially 40 parts that of an incandescent lamp. 7 of calcium fluoride to 10 parts of strontium fluoride, the carbon electrode being characterized by 80 1. A core for carbon electrodes comprising the fact that, when burned as the positive eleccalcium fluoride 40 parts, strontium fluoride 10 trode in an arc of high intensity, the arc has a parts, sodium or potassium silicate 5 parts, carbon color value similar to that of an incandescent flour parts, and tar. suflicient to bind. light.

10 2. A cored carbon electrode for use in a high I lvlERRflih J. DORCAS. 

